Date of this Version
Published in Permafrost: Proceedings of the 8th International Conference on Permafrost 2003, Lukas U. Arenson, Marcia Phillips, & Sarah M. Springman, eds. (CRC Press, 2004)
Sand-wedge polygons on upland surfaces beneath thin loess in northeastern Nebraska record the existence of permafrost around the margin of the Wisconsinan glacier at its maximum advance. Strong unidirectional wind not only kept the upland surfaces free of snow, allowing frost to penetrate deeply and thermal contraction cracks to develop, but also dessicated the surface material so that frost action and sublimation of pore ice could loosen surface material. The strong NW-SE winds deflated soils from upland surfaces, made ventifacts of the cobbles in the lag that remained and created fields of yardangs oriented NW-SE. Sand derived from the soils and underlying till was carried only a short distance to fill the thermal contraction cracks and in some places leave a thin sheet of sand covering the former surface.